1. Field of the Invention
The present invention relates to a rotor magnet and a motor.
2. Description of the Related Art
As is well known, use of a permanent magnet is widely diversified and in the use, a permanent magnet maintains an important position as a constituent element of an electronic apparatus, particularly, a small-sized motor, particularly as a rotor magnet. The performance of a permanent magnet has been advanced year by year and a magnetic material thereof, has been changed from an alnico magnet to a ferrite magnet, further, in recent years, materials having a larger magnetic flux density such as a samarium-cobalt (SmCo) series magnet or a neodymium-iron-boron (NdFeB) series magnet have been adopted.
It is well-known that as these permanent magnets a sintered body constituted by sintering a composite body derived from metal elements or a resin bonded magnet constituted by kneading both of a magnetic powder and a resin powder with the resin powder as a binder and molding a mixture thereof have been employed. See Japanese Patent Publication No. 87634/1994.
Generally, a magnetic property of a magnetically anisotropic magnet is regarded to be higher than that of a magnetically isotropic magnet. A maximum energy product (BHmax) of an anisotropic NdFeB series magnet is larger than that of an anisotropic SmCo series magnet and therefore, higher magnetic energy can be provided even when the magnet is formed in a small shape and the magnet can be downsized when the same magnetic energy is intended to be obtained. In a different view, in the case of using the magnet of the anisotropic SmCo series, the magnet cannot be downsized in comparison with the anisotropic NdFeB series magnet.
However, when the anisotropic NdFeB series magnet is used as a rotor magnet for a motor, since a magnetic powder thereof is large (size: 100 through 200 μm), there causes a dispersion in a density of the magnetic powder in the magnet and accordingly, there causes a dispersion in magnetic fluxes generated at respective poles.
That is, when a rotor magnet is intended to be downsized, there poses a problem in which there is increased a dispersion in poles of a rotor which should not be present in the motor.